Magpies vs. Crows

[sherlockian]

Why do crows continually harass magpies? There are a pair of magpies in an adjacent garden trying to nest, but one crow keeps visiting and attacking them and this can go on for hours at a time. I gather this behaviour is common, but what is the crow's motivation? I've never seen a crow in the area at all before (seaside - thousands of seagulls but no crows!). Thanks.

[Lonnie]

I would say its because,

Even though they are the same family, they are rivals for the same food, eggs, young chicks etc.

[Annlinda]

Magpies take eggs and young birds. They are a menace our farmer friend shoots them and he has more song birds on the farm now

[tiny e.a]

maybe magpies are always dissing crows mammas